Rapid steam hydrolysis of wood chips with continuous condensate/product removal was investigated as a biomass pretreatment similar to steam explosion. Steam was introduced at the top of a pressurized reactor containing mixed southern hardwood chips while steam condensate and partible products were removed at the bottom of the reactor. A reaction time of one minute was employed for isothermal steaming runs from 160-280°C. Fractionation of wood occurred at temperatures above 200°C as hemicellulose and lignin began to appear in the steam condensate fraction, leaving a cellulose-rich fraction in the steaming reactor. At high temperatures cellulose was not degraded as much as it was in steam explosion at the same temperature, presumably due to the removal of acetic acid as it is formed. Lignin extracted from the solid residue appeared particularly reactive as determined by nitrobenzene oxidation and pyrolysis/gas chromatography. Lignin collected in the steam condensate was also very reactive, presumably due to its rapid cooling after being removed from the reactor.